Tunable CHA/AEI Zeolite Intergrowths with A Priori Biselective Organic Structure‐Directing Agents: Controlling Enrichment and Implications for Selective Catalytic Reduction of NOx

Abstract A novel ab initio methodology based on high‐throughput simulations has permitted designing unique biselective organic structure‐directing agents (OSDAs) that allow the efficient synthesis of CHA/AEI zeolite intergrowth materials with controlled phase compositions. Distinctive local crystallographic ordering of the CHA/AEI intergrowths was revealed at the nanoscale level using integrated differential phase contrast scanning transmission electron microscopy (iDPC STEM). These novel CHA/AEI materials have been tested for the selective catalytic reduction (SCR) of NOx, presenting an outstanding catalytic performance and hydrothermal stability, even surpassing the performance of the well‐established commercial CHA‐type catalyst. This methodology opens the possibility for synthetizing new zeolite intergrowths with more complex structures and unique catalytic properties.

Step 4: 50 mmol of the iodide form of the template was dissolved in 110 ml of water. Then, 100 g of anion-exchange resin (Amberlite IRN-78) was added to the solution and kept under stirring for 24 h. Finally, the solution was collected by filtration and the obtained hydroxide form of the OSDA presented an exchange efficiency of at least 95%.

2.1.3.-Synthesis of N-ethyl-N-methyl-diisopropyl-ammonium hydroxide (OSDA3)
In a round-bottom flask, 278 mmol of N-ethyl-diisopropylamine (35.94 g) was dissolved in 150 ml of diethyl ether. The resulting solution was cold in an ice-bath and under continuous stirring, and 707 mmol of methyl iodide (100.32 g) was added dropwise in three aliquots over a 24 h period. Then, the solution was left to react one week at room temperature under stirring. When the reaction was completed, N-ethyl-N-methyl-diisopropyl-ammonium iodide precipitated as a white solid. The product was isolated by filtration and dried. 50 mmol of the iodide form of the template was dissolved in 110 ml of water. Then, 100 g of anion-exchange resin (Amberlite  was added to the solution and kept under stirring for 24 hours. Finally, the solution was collected by filtration and the obtained hydroxide form of the OSDA presented an exchange efficiency of at least 95%.

2.1.4.-Synthesis of 1-ethy-1-isopropylpyrrolidin-1-ium hydroxide (OSDA4)
A) Synthesis of 1-isopropylpyrrolidin-1-ium bromide 100 mmol of pyrrolidine (7.11 g) was dissolved in 100 ml of 2-propanol and then 250 mmol (30.75 g) of 2-bromopropane was added through small aliquots under stirring. The resulting solution was heated to 70C and allowed to react for 24 h. Afterwards, the reaction mixture was cooled down to room temperature, and an ethyl acetate-acetone mixture was added to precipitate the organic salt. Finally, 1-Isopropylpyrrolidin-1-ium bromide was isolated by filtration and recrystallized.

B) Synthesis of 1-isopropylpyrrolidine
74 mmol of 1-isopropylpyrrolidin-1-ium bromide (14.38 g) was dissolved in 100 ml of distilled water, and 74 mmol of sodium hydroxide (2.96 g) was added under stirring. The resulting solution was kept one hour at room temperature. A biphasic mixture was obtained, in which 1-isopropylpyrrolidine was present at the top phase. The compound was separated by decantation and, a liquid-liquid extraction was carried out with chloroform (2 x 50 ml) on the remaining aqueous phase to recover part of the dissolved amine. The two organic parts were combined, dried over anhydrous magnesium sulphate, filtered to remove the inorganic salt and, finally, the solvent was evaporated. 1-Isopropylpyrrolidine was obtained as a thick yellow liquid. The resultant gel was charged into a stainless steel autoclave with a Teflon liner. The crystallization was then conducted at 150C for 7 days under dynamic conditions. The solid product was filtered, washed with abundant water, and dried at 100C. The solid was calcined at 580C for 5 h in air to remove the occluded organic molecules. The resultant gel was charged into a stainless steel autoclave with a Teflon liner. The crystallization was then conducted at 135C for 6 days under dynamic conditions. The solid product was filtered, washed with abundant water, and dried at 100C. The solid was calcined at 580C for 5 h in air to remove the occluded organic molecules.

2.3.-Cu-exchange treatments
The calcined solids were first exchanged with a 2M aqueous solution of ammonium nitrate (NH 4 Cl, Sigma-Aldrich, 99% by weight) with a liquid/solid ratio of 10, maintaining the mixture at 80C for 2 hours under agitation. Afterwards, the solids were recovered by filtration.

2.4.-Hydrothermal ageing treatments of Cu-exchanged zeolites
The Cu-exchanged zeolites were subjected to a hydrothermal treatment at 750 or 850C using a 300 ml/min flow rate with 10% water, 10% of O 2 and balanced with nitrogen for 13 hours.

2.5.-Characterization
Powder X-ray diffraction (PXRD) measurements were performed with a multi sample Philips X'Pert diffractometer equipped with a graphite monochromator, operating at 40 kV and 35 mA, and using Cu Kα radiation (λ = 0.1542 nm).
Chemical analyses were carried out in a Varian 715-ES ICP-Optical Emission spectrometer, after solid dissolution in HNO 3 /HCl/HF aqueous solution. 27 Al MAS NMR spectra were recorded at room temperature with a Bruker AV 400 spectrometer at 104.2 MHz with a spinning rate of 10 kHz and 9 o pulse length of 0.5 μs with a 1 s repetition time. 27 Al chemical shift was referred to Al 3+ (H 2 O) 6 .
Nitrogen adsorption isotherms at -196C were measured on a Micromeritics ASAP 2020 with a manometric adsorption analyser to determinate the textural properties of the samples.
The morphology of the samples was studied by field emission scanning electron microscopy (FESEM) using a ZEISS Ultra-55 microscope.
The sample was prepared for transmission electron microscopy (TEM) studies using ultra microtomy in order to obtain thin sections and to access the desired crystallographic direction for imaging. The zeolite powder was dried in oven overnight and embedded in an epoxy resin (Agar Low Viscosity Resin) which was hardened at 60C for 24 h. Sectioning was performed using a Leica Ultracut UCT with a 45 diamond knife from Diatome to an estimated thickness of 50 nm. After cutting, the sections were transferred to holey carbon coated copper grids. Scanning transmission electron microscopy (STEM) images were obtained using a ThermoFisher ThemisZ double aberration-corrected TEM using an integrated differential phase contrast (iDPC) detector. The TEM was operated at an accelerating voltage of 300 kV. The image contrast was formed. A high-pass filter was applied to the iDPC images in order to reduce low frequency noise. The STEM images were acquired using an electron beam dose current of 20 pA, a convergence angle of 16 mrad and a dwell time of 10 µs. The sample was dried in vacuum at 180C during 3 h prior to data acquisition in order to remove adsorbed water and enhance stability. The SED data were acquired using the in-house build software suite St4DeM, capable of acquiring 300 frames/s using the Gatan Oneview camera with software synchronization. St4DeM is written within the Digital Micrograph SDK environment and is successfully tested with Thermo Fischer 300 kV Themis and JEOL 2100F microscopes. [12] The SED data was analyzed using Pyxem. [13] NH 3 -TPD experiments were carried out in a Micromeritics 2900 apparatus. A calcined sample (100 mg) was activated by heating to 400°C for 2 h in an oxygen flow and for 2 h in argon flow. Subsequently, the samples were cooled down to 176°C, and NH 3 was adsorbed. The NH 3 desorption was monitored with a quadrupole mass spectrometer (Balzers, Thermo Star GSD 300T) while the temperature of the sample was ramped at 10°C min -1 in helium flow.

2.6.-NH3-SCR catalytic test
The catalytic activity was evaluated for the catalytic reduction of NOx with NH 3 in a fixed bed, quartz tubular reactor with 1.  (1)- (3): where "in" corresponds to the inlet concentration, and "out" the outlet concentration.